[R] step halving factor reduced below minimum

[Douglas Bates]

sw289 at columbia.edu writes:

> Dear Splus and R users:
> I have a problem in fitting a NLME model, the error message is:
> 
> "step halving factor reduced below minimum in PNLS step"
> 
> What does it mean and how to fix the problem, could anyone help me 
> about it?
> 
> Any suggestion/help would be greatly appreciated.

Turn on the verbose option (i.e. add verbose = TRUE to the nlme call)
to see what is happening to the parameter estimates during the
iterations.  That should give you a clue as to why the estimation
algorithm is not converging.